Accelerated weathering devices are used by a number of industries to simulate a product's resistance to outdoor environmental stresses such as temperature, moisture, and exposure to terrestrial solar radiation. A manufacturer of a given product may warranty the performance of a product for a specified lifetime based on the results of the accelerated weathering. Although temperature, humidity, and solar radiation are all factors that affect the degradation of a product, exposure to solar radiation is one of the more influential factors in weathering. Ultraviolet rays are known to degrade polymers and other materials over time.
Since accelerated weathering devices employ an artificial light source, among the more difficult tasks in the manufacture of accelerated weathering devices is to provide a spectral power distribution of artificial light that matches natural sunlight on earth. Approximating spectral power of sunlight is typically accomplished by passing illumination from the artificial light source through one or more optical filters. Wavelengths of light that are present in artificial light when passed through optical filters and not present in terrestrial sunlight have been found to change the balance of degradation and stabilization reactions. To the extent possible, these wavelengths of light should be eliminated from test protocols.
Optical filters and illuminators comprising such optical filters used in accelerated weathering devices are subject to harsh light intensity as well as thermal and moisture loads. Although many of the optical filters and illuminators currently available are durable to some extent, industry would find advantage in improvements of optical filters and illuminators that are amenable to extending their durability.